Assessment and Remediation of Contaminated Sediments (ARCS) Program
Table of Content
- Chapter 1
- Chapter 2
- Chapter 3
- Chapter 4
- Chapter 5
- Chapter 6
- Chapter 7
- Chapter 8
- Chapter 9
- Chapter 10
- Chapter 11
- List of Figures
- List of Tables
Remediation Guidance Document
US Environmental Protection Agency. 1994. ARCS Remediation Guidance Document. EPA 905-B94-003. Chicago, Ill.: Great Lakes National Program Office.
Table of ContentsDISPOSAL TECHNOLOGIES
- DESCRIPTIONS OF TECHNOLOGIES
- SELECTION FACTORS
- ESTIMATING COSTS
- ESTIMATING CONTAMINANT LOSSES
Disposal is the placement of material into a site, structure, or facility on a temporary or permanent basis. The disposal component of a remedial alternative may include the disposal of the dredged sediments or the disposal of residues from pretreatment and/or treatment components. This chapter briefly discusses the temporary storage of sediments and residues, but focuses primarily on permanent disposal.
Disposal is a major component of virtually any sediment remedial alternative, except for nonremoval alternatives. The site or location used for disposal may also be used to implement other components, including pretreatment, treatment, and residue management. The identification of disposal sites is often the most controversial part of remedial planning and design.
This chapter provides descriptions of technologies for the disposal of contaminated sediments. Discussions of the factors for selecting from the available technology types and techniques for estimating costs and contaminant losses are also provided.
Technologies for the disposal of contaminated sediments and residues from pretreatment or treatment components include open-water disposal, beneficial use, and confined (diked) disposal.
A detailed literature review of the disposal technologies is provided in Averett et al. (in prep.). The general features of these technologies are summarized in Table 8-1.
Dredged sediments and the residues from pretreatment or treatment technologies may be suitable for the following types of open-water disposal: unrestricted, open-water disposal; level-bottom capping; and contained aquatic disposal.
Open-water disposal is the most common disposal technology used for uncontaminated dredged material worldwide. Approximately 2.3 million m of sediments are dredged and discharged into the Great Lakes annually (IJC 1982). Most of these materials are discharged into shallow waters (<18 m) within a few kilometers of the dredging location. Some materials are discharged into nearshore waters to "feed" the littoral drift and nourish eroded beaches. Materials are typically discharged from bottom-dump scows and hoppers, or from dredge pipelines, as shown in Figure 8-1.
Capping is a disposal technology that has been used for contaminated dredged material in ocean and estuarine waters. Contaminated materials are placed on the bottom and then covered with a cap of clean materials to isolate the contaminants both physically and chemically (Palermo et al., in prep.). Level-bottom capping involves the placement of the contaminated materials on a relatively flat surface, forming a mound, as shown in Figure 8-2. The capping material is placed on top of the mound. The thickness and material characteristics of the cap must be carefully designed to ensure that it isolates the contaminants and can withstand the forces of scour and erosion within acceptable maintenance (replenishment) requirements.
Contained Aquatic Disposal
Contained aquatic disposal is a type of capping in which the contaminated materials are placed into a natural or excavated depression or trench, as shown in Figure 8-2. This depression or trench provides lateral containment of the contaminated material. The design and placement of the cap is essentially the same as for the level-bottom cap. One advantage of contained aquatic disposal is that without a mound the cap may be more resistant to erosion and require less maintenance. The depression for contained aquatic disposal can be excavated using conventional dredging equipment or natural depressions or previously mined pits (sand mining from near-shore areas has occurred in the Great Lakes). Uncontaminated material excavated from the depression can subsequently be used for the cap. Palermo et al. (in prep.) provides detailed guidance on contained aquatic disposal and cap planning and design.
Dredged sediments and solid residues from pretreatment or treatment technologies may be suitable for a variety of beneficial and productive uses, including beach nourishment, land application, general construction fill, and solid waste management.
The feasibility of these disposal technologies depends on the physical properties of the material, the type and level of contamination, and the local need for materials for these or other beneficial uses. A general discussion of beneficial uses is provided in Averett et al. (in prep.). The Corps' engineering and design manual, Beneficial Uses of Dredged Material (USACE 1987a), should be consulted for more detailed information.
Shoreline erosion is a chronic problem throughout the Great Lakes and is responsible for damage to public and private properties and the destruction of valuable habitat (IJC 1993). About 10-20 percent of the sediments dredged by the Corps from Great Lakes harbors and tributaries are used to nourish existing beaches or are placed into shallow waters to reform or renourish eroded beaches and shorelines. In most cases, beach nourishment is accomplished using hydraulic (cutterhead) dredging with pipeline transport to a nearby beach or shoreline. Sediments are mounded on the beach and the pipeline discharge is moved periodically to distribute the sediments as desired. Residues of pretreatment or treatment technologies found suitable for beach nourishment would have to be transported from the pretreatment or treatment location, offloaded, and possibly redistributed using earth-moving equipment.
Sediments and residues from pretreatment or treatment technologies may be used to replace eroded soils or amend marginal soils for agriculture, horticulture, and forestry. Materials such as silt or sandy silt can be readily incorporated into existing silt and clay soils, and may improve drainage and add nutrients (USACE 1987a). Substantial quantities of the sediments dredged from navigation channels on the Mississippi River, Ohio River, and Illinois River are discharged directly onto adjacent fields and incorporated into existing agricultural soils (USACE 1987a). In most cases, the sediments are dredged hydraulically and transported to farm fields by pipeline. Sediments or residues might also be reclaimed from a CDF or treatment operation and transported to the application site.
General Construction Fill
Sediments and treatment residues may be used as a fill material for a variety of construction projects. Some dredged material has poor foundation qualities; thus its applicability to a particular construction project would depend on the physical and engineering properties of the material and the specific requirements of the project. Sandy sediments were reclaimed from a CDF in Duluth, Minnesota, and used for road construction fill (Bedore and Bowman 1990). Some sediments/residues may be suitable for use in the production of concrete (see discussion of solidification in Chapter 6).
Solid Waste Management
Sediments and treatment residues may be used by municipal or commercial landfills for dike and cap/cover construction and/or as daily cover. Most landfills will only accept materials that have low organic content and are dewatered sufficiently to pass a paint filter test (EPA Method 9095, SW-846; USEPA 1991h). Sediments reclaimed from a CDF and residues from treatment operations might be transported by truck to a nearby landfill for use. At the landfill, the sediments/residues could be stockpiled for later use and spread out using conventional earth-moving equipment. Some landfills will offer a discounted rate for disposal of contaminated sediments if the sediments can be used for daily cover.
Confined disposal is the placement of dredged material into a site or facility designed to contain the material and control contaminant loss. The two types of confined disposal are commercial landfills and CDFs.
Technically, the designs of these facilities may be quite similar. The primary difference between them is the types of materials for which they are constructed. Commercial and municipal landfills may be constructed to receive a variety of wastes, including municipal and commercial refuse, sewage sludge, construction debris, industrial solid wastes, contaminated soils, and other materials. In the Great Lakes, CDFs have been constructed solely for the disposal of contaminated dredged material.
The difference in materials can have major effects on the operation of these facilities. Most solid waste landfills are designed to accept a physically heterogeneous mixture of materials that has very little water. A CDF is designed to receive a physically homogeneous material that may be 10- to 50-percent solids by weight.
A general discussion of confined disposal is provided in Averett et al. (1990 and in prep.). The Corps' engineering and design manual, Confined Disposal of Dredged Material (USACE 1987b), should be consulted for more detailed information. In addition to the above disposal technologies, temporary storage facilities for sediments awaiting treatment or residues awaiting transport are discussed below.
Landfills are operated by municipalities and commercial interests for the disposal of various wastes. Landfills are categorized by the types of wastes they accept and the laws regulating them. Some landfills are constructed for specific materials, such as municipal sewage sludge and construction wastes. Most solid waste landfills will accept all types of materials that are not regulated as RCRA-hazardous or TSCA-toxic materials. There are a relatively limited number of landfills that are licensed to receive RCRA-hazardous and TSCA-toxic materials. Only a few licensed chemical waste landfills in the country can accept TSCA-regulated materials. There are 86 commercial RCRA-regulated land disposal facilities in the United States.
A landfill is constructed in an existing or excavated depression or using earthen dikes. The design of a landfill involves one or more of the following types of controls to reduce the loss of contaminants: barrier systems, caps/covers, drainage systems, and leachate collection systems.
The types of controls at a landfill reflect the nature and level of contamination in the materials approved for disposal and the regulatory requirements of the permitting authority. Landfills for RCRA-hazardous and TSCA-toxic materials have more sophisticated and redundant control systems. A comparison of the control systems of solid waste (RCRA Subtitle D), hazardous waste (RCRA Subtitle C), and chemical waste (TSCA) landfills is shown in Figure 8-3.
Contaminated sediments that have been dewatered and residues from pretreatment or treatment technologies may be disposed in commercial or municipal landfills. The current use of commercial landfills for disposal of contaminated sediments is generally limited to small quantities of materials from marine construction projects (e.g., bridge rehabilitation, pipeline and cable crossings). Some landfills have used sediments for daily cover or for the construction of interior dikes and caps/covers.
Confined Disposal Facilities
For many years, dredged material from navigation projects in which open-water disposal was impractical has been disposed in diked structures. The purpose of the diked structures was to promote settling so that the sediments would not return to the waterway and need to be dredged again. It was not until the 1960s that dredged material was confined because of environmental concerns. In 1967, the Corps, in cooperation with the Federal Water Pollution Control Administration (the predecessor of the USEPA), initiated a 2-year pilot investigation of alternative methods for dredged material disposal in the Great Lakes (USACE Buffalo District 1969). The first CDFs on the Great Lakes were constructed as part of this program.
CDFs are the most widely used disposal technology for contaminated sediments from both navigation dredging and remediation projects. Since the 1960s, approximately 50 CDFs have been constructed around the Great Lakes, in the United States and Canada, for dredged material from navigation projects. About two-thirds of these facilities are lakefills, constructed with stone dikes. The remainder are upland facilities, constructed with earthen dikes or placed within existing or excavated depressions. CDFs around the Great Lakes currently contain sediments dredged over periods of 10 or more years, have capacities from less than 38,000 to more than 3 million m, and have areas from a few to several hundred hectares (Miller 1990).
The goal of confined disposal is to isolate and contain sediment contaminants. Because of the nature of dredged material, a CDF must have features of both a wastewater treatment facility and a solid waste landfill to effectively meet this goal. A CDF that receives sediments that are hydraulically dredged or transported must provide for the settling of the sediments and primary treatment of the effluent water (see Chapter 9). Through effective solids retention, a CDF can retain most of the sediment contaminants (Saucier et al. 1978). Most CDFs are capable of retaining more than 99.9 percent of suspended solids discharged in hydraulic slurries.
A CDF must also provide for the dewatering of sediments to facilitate consolidation and compaction and to maximize the usable space in the facility (as discussed in Chapter 6). CDFs have been constructed with the same types of controls used in commercial landfills to limit contaminant loss, although some of these controls may be less feasible at in-water CDFs and the efficiency of others may be affected by fine-grained sediments within the CDF.
Temporary Storage Facilities
Remedial alternatives that involve treating sediments and disposing of the residues at locations remote from the treatment site will usually require a facility for the temporary storage of sediments and/or residues. Temporary storage may be necessary for a number of reasons and purposes, including:
- Treatment processes cannot keep pace with dredging operations
- It is more economical to store residues and transport them all at one time
- Residues must be separated for different disposal locations or by different methods
- A secure land area is needed for or to support pretreatment or treatment operations
A temporary storage facility is usually part of the property where pretreatment or treatment operations are conducted, and might be divided into two or more compartments or cells to accommodate the different types of sediments and residues. The facility may also be part of a CDF used for the permanent disposal of residues. Locations where materials are transferred from one means of conveyance to another (e.g., a site where sediments are removed from a barge and placed in truck trailers) are not included in this category.
The types of environmental controls (i.e., barrier and leachate collection systems) constructed at the temporary storage facility would depend on the physical properties and contaminant concentrations in the sediments and/or residues to be stored.
Within the evaluation and decision-making process discussed in Chapter 2, disposal technologies must be screened for feasibility and compatibility with other components. Factors that can be used to determine the suitability of a disposal technology for a specific application are discussed in this section; these factors are summarized in Table 8-2.
The most critical factors in determining the feasibility of a disposal alternative are the availability and location of a disposal site. These factors are common to all disposal technologies (and are therefore not shown in Table 8-2). The location of a potential disposal site, its distance from the dredging location, and its accessibility from existing transportation routes are factors that may limit the choice of dredging and transportation equipment and increase transportation costs (see Chapter 5, Transport Technologies).
The boundaries of the area for disposal site evaluation should be established with some consideration of reasonable travel distances. In some cases, there may be reasons for limiting the site consideration to certain political boundaries. For example, if the project proponent is a city or county government, they may require that the disposal site be within their jurisdiction. The availability of sites or facilities for the various disposal technologies is highly site specific. The task of identifying potential sites is best conducted with a team of representatives from local governmental and public organizations who are familiar with the region.
The discharge of dredged or fill materials into waters of the United States is regulated under section 404 of the Clean Water Act. The unrestricted discharge of contaminated dredged material is prohibited; therefore, sediments that have been removed as part of a remediation project are not likely to be suitable for unrestricted, open-water disposal. However, the solid residues from sediment pretreatment or treatment processes (treated sediments) may be suitable for such disposal.
The acceptability of this disposal technology can be determined through the application of a technical framework developed by the USEPA and the Corps for evaluating the environmental effects of dredged material management alternatives (USACE/USEPA 1992). This framework, introduced in Chapter 2 (Figure 2-1), was developed to address the regulatory requirements under section 404 of the Clean Water Act and NEPA.
The framework begins with an evaluation of the dredging and disposal needs. Disposal alternatives are then identified and screened. The detailed assessment of open-water disposal includes the testing of proposed dredged or fill materials to show that they are not contaminated and are suitable for open-water disposal. The Corps/USEPA framework for testing and evaluation for open-water disposal is shown in Figure 8-4. National guidance (USEPA/USACE 1994) and regional guidance specific to the Great Lakes (USEPA/NCD 1994) are available on testing and evaluation procedures for making this determination. The framework integrates physical, chemical, and biological effects tests to make a decision.
Guidance on the designation of disposal sites in the ocean has been prepared by the USEPA and the Corps (USACE/USEPA 1984; USEPA 1986a; Pequegnat et al. 1990). No comparable guidance for the selection of disposal sites in inland waters has been developed; however, the ocean disposal site designation guidance is generally applicable with a few exceptions. Factors to consider in selecting a disposal site include, but are not limited to:
- Currents and wave regime
- Water depth and bathymetry
- Potential changes in deposition or erosion patterns
- Chemical and biological characteristics of the site
- Other uses of the site that may conflict with disposal
Most of the open-water disposal sites around the Great Lakes are dispersive, meaning that materials discharged are rapidly dispersed and transported away from the disposal site. The most common concern with unrestricted, open-water disposal in the Great Lakes, other than the contamination, is the potential impact on aquatic habitat and water supply intakes.
The placement of contaminated material into waters of the United States can be permitted under section 404 (40 CFR 230.60(d)) if "constraints are available to reduce contamination to acceptable levels within the disposal site and to prevent contamination from being transported beyond the boundaries of the disposal site." The Corps/USEPA framework for open-water disposal testing and evaluation (Figure 8-4) considers capping and other benthic controls.
Capping may be suitable for sediments or residues with moderate levels of contamination. Grossly contaminated materials are not likely to be suitable for capping. The determination of suitability requires the concurrence of the Corps and the USEPA on controls and monitoring requirements.
The Corps has developed guidance on capping contaminated dredged material (Palermo et al., in prep.), and additional guidance on in situ capping in the Great Lakes is being developed under the ARCS Program (Palermo and Reible, in prep.). The major elements in the planning and design of a capping disposal project are:
- Characterization of contaminated and capping sediments
- Selection of capping site
- Selection of placement equipment and techniques
- Determining cap thickness
- Determining maintenance and monitoring requirements
Each of these elements is discussed below.
Characterization of Contaminated and Capping Sediments--Physical properties of the contaminated sediments and potential capping materials that need to be tested include visual classification, natural solids content, plasticity indices, organic content, grain size distribution, specific gravity, and Unified Soil classification (Palermo et al., in prep.). Standard methods for these tests are provided in the Corps' soils testing manual (USACE 1970).
Selection of Capping Site--Potential capping sites must be evaluated with consideration of the same factors as for unrestricted, open-water disposal. In addition to these considerations, the capping site should be in a relatively low-energy environment with little potential for erosion of the cap (Palermo et al., in prep.). This may require that sites be in deeper waters than are commonly used for most unrestricted disposal in the Great Lakes.
Selection of Placement Equipment and Techniques--Conventional dredging and transport equipment have been used for capping. The objective is to reduce water-column dispersion and bottom spread to the greatest extent possible. Cap material must be placed so that it does not displace or mix with the contaminated sediments. Specialized equipment has been developed and demonstrated for precise placement of contaminated materials on the bottom and the application of a cap (Palermo et al., in prep.).
Determining Cap Thickness--The cap must be designed to chemically and biologically isolate the contaminated materials from the aquatic environment. Cap thickness is determined by the physical and chemical properties of the contaminated sediments and capping material, the potential bioturbation by aquatic organisms, and the potential for consolidation and erosion of the cap material (Palermo et al., in prep.). A capping effectiveness test has been developed to determine the thickness required for chemical isolation (Sturgis and Gunnison 1988).
Determining Maintenance and Monitoring Requirements--A monitoring program is needed to ensure that the contaminated material and cap are placed as intended and that the cap is effectively isolating the contaminants (Palermo et al., in prep.). Monitoring is also necessary to determine when additional capping material or other maintenance is required.
Contained Aquatic Disposal
The major requirements and design elements for contained aquatic disposal are generally the same as those discussed for level-bottom capping.
The acceptability of sediments or treated sediments for beneficial use is addressed in the Corps/USEPA technical framework introduced in Chapter 2 (USACE/USEPA 1992). In most cases, the suitability of a sediment will depend on its physical properties as well as its contaminant properties. A beneficial use typically requires specific physical properties (i.e., coarse- or fine-grained, low or high organic content).
Most beneficial use technologies have some land requirements to be provided by the project sponsor or proponent. Lands may be purchased for use, or a temporary easement or right-of-way may be obtained from the existing landowners. In some cases, a fee or other consideration may be paid to the landowner. Beneficial use is most feasible where the conditions of the site are improved and the landowner derives benefits from the sediments.
Disposal by beach nourishment is regulated under section 404 of the Clean Water Act, and contaminated sediments are not likely to be suitable for beach nourishment. However, sediments that have been treated may be suitable for such disposal. The suitability of a material for beach nourishment is generally determined by its physical properties, particularly grain size distribution. Evaluation of the suitability of sediments for beach nourishment is usually made by comparison with existing beach sand. The general rule of thumb is that nourishment material should be as coarse, if not coarser, than native beach material (Johnson 1994). Uncontaminated treatment residues that have a high percentage of sand and gravel, such as those from physical separation technologies (see Chapter 6), are most likely to be suited for this use.
The application of sediments and treated sediments to upland sites may be suitable for materials with moderate levels of contamination. This type of land application is regulated by State or local statutes. Materials including any associated water discharges that are returned to a stream, river, or lake would be regulated under section 404 of the Clean Water Act.
The suitability of a material for agricultural or other land applications is determined by its physical and chemical characteristics. The physical requirements are often determined by the needs of the existing soil to be amended. Sandy materials may be needed to enhance drainage in clay soils while silty materials may be needed to supplement sandy soils. Other suitability factors include the need for pH adjustment (with lime) and control of weed infestation (USACE 1987a).
Sediments and treated sediments with some types and concentrations of contaminants may still be suitable for land application. The mobility or availability of contaminants through appropriate pathways must be considered (USACE/USEPA 1992). Laboratory tests to evaluate the potential for contaminant leaching (Myers and Brannon 1991) and bioaccumulation in plants and animals (Folsom and Lee 1985; Simmers et al. 1986) have been developed for dredged material. Materials with acceptable ranges of contaminant mobility and bioavailability may be used for agricultural lands, nonconsumptive uses (i.e., horticulture and silvaculture), or landscaping.
General Construction Fill
The regulations, requirements, and suitability factors for use of sediments and treated sediments as construction fill are generally the same as for land applications. Potential disposal sites may be identified through construction proponents (e.g., city, county, or State departments of highways, or public works) or construction contractors. The physical requirements for construction fill will depend on the application. Construction contractors are likely to require that materials be suitably dewatered and free of debris, and that regulatory agencies have preapproved the material for use. The laboratory tests for measuring the leaching and bioaccumulation potential of contaminants (cited for land application) may be appropriate, depending on the application.
Solid Waste Management
The use of sediments or treated sediments in landfill management is regulated by the State and Federal statutes under which the landfill is permitted. Contaminated materials are generally suitable for use as daily cover and for construction of internal dikes, providing they meet certain physical requirements. For example, materials must be sufficiently dewatered to pass the paint-filter test (EPA Method 9095, SW-846; USEPA 1991h) and free of debris. Contaminated materials may also be suitable for use as part of the landfill cap or cover, provided they will not promote bioaccumulation in the vegetation grown on it. However, some states may have restrictions on the use of "waste" materials for landfill caps and covers.
Municipal and commercial landfills are available that can accept most types of contaminated sediments and treatment residues. The suitability of a material for a landfill is determined by the type and concentrations of contaminants and the regulatory requirements (as addressed in Chapter 2). Most contaminated sediments and treatment residues are not RCRA-hazardous or TSCA-toxic and are suitable for disposal in municipal or commercial solid waste or sanitary landfills.
Location and cost are the primary factors in identifying potential landfills for disposal. While there are numerous commercial solid waste and sanitary landfills, there are only 86 commercial RCRA landfills and 4 commercial TSCA landfills in the country (Petrovski 1994). Another factor to be considered is the remaining capacity of the landfill. A remediation project with a large volume of contaminated sediments to dispose could overwhelm a single landfill, and the rapid loss of landfill capacity might have adverse impacts on regional waste management practices.
The only requirements for the material's physical characteristics for landfill disposal are related to solids content. RCRA requires that all materials disposed to a solid waste or RCRA-hazardous landfill pass the paint-filter test (EPA Method 9095, SW-846; USEPA 1991h); however, there are no published data on the paint-filter test using dredged sediments, and it is not known at what solids content sediments are likely to fail.
Confined Disposal Facilities
Most of the contaminated sediments dredged from navigation and remediation projects are placed in CDFs. A CDF may be used solely for the disposal of contaminated sediments, or it may also serve as the staging area where pretreatment, treatment, and residue treatment/disposal are implemented. A CDF can therefore serve as the base upon which preliminary designs for other remedial alternatives are developed, and as a baseline for comparing the costs and impacts of alternatives.
Regulation--The construction and operation of a CDF may be regulated under a number of environmental laws. The construction of CDFs in water or wetlands is regulated under section 404 of the Clean Water Act. The effluent from a CDF, if discharged to waters of the United States, is also regulated under section 404. If the materials to be disposed (or handled) in the CDF are TSCA- or RCRA-regulated, the facility must be permitted as appropriate. RCRA (40 CFR 268) requires the treatment of hazardous wastes prior to land disposal. Other site-specific State and local statutes may also apply.
Currently, the Corps has no policy concerning the disposal of sediments or treatment residues from remediation projects in existing CDFs. CDFs operated by the Corps were constructed for specific navigation projects, and there is limited capacity in these facilities. Materials dredged by industries, municipalities, or others from the slips and docking areas adjacent to the navigation channel are routinely disposed in these existing CDFs, at cost.
The suitability of materials for disposal in an existing CDF is determined by the level of contamination. Materials with levels of contamination comparable to those of sediments for which the facility was constructed are generally acceptable for disposal. The disposal in a CDF of materials that are more highly contaminated may require that the section 404 evaluation and section 401 water quality certification for the facility be modified. In addition, the EIS for the CDF may have to be revised if sediments other than those evaluated in the original EIS are proposed for disposal.
Physical Properties--There are generally no limitations on the physical characteristics of sediments and residues disposed in a CDF. Most facilities are designed to accept materials that have been dredged hydraulically or mechanically and contain variable amounts of oversized material and debris, with a few exceptions. For example, some small CDFs and larger facilities that are nearly full do not have the capacity to handle hydraulically dredged material because they cannot provide adequate settling times for efficient solids retention. Mechanical dredging and transportation may be required if the dredged material is to be disposed in such facilities.
Contaminant Properties--The suitability of a material for disposal in a CDF and the design of the facility are primarily determined by the nature of contamination in the sediments and the potential for contaminant release. The Corps/USEPA technical framework, discussed in Chapter 2, includes a framework for testing and evaluation for confined disposal, as shown in Figure 8-5. This framework identifies the following contaminant pathways of concern: effluent, surface runoff, groundwater leachate, and plant and animal uptake.
The Corps/USEPA framework uses a series of laboratory tests to evaluate the potential contaminant loss or migration from the sediment disposed in a CDF through these pathways. Specific requirements for these tests, as well as approximate costs for analysis, are summarized in Table 8-3.
The modified elutriate, surface runoff, and plant/animal uptake testing protocols are well established and have been verified in the field. The leachate tests have been developed, but no field confirmation has been conducted. A contaminant pathway (not shown in Figure 8-5) that has only recently been considered for sediments is volatile loss to the atmosphere. A test to evaluate volatilization losses from dredged sediments is still in development (Semmler 1990). Sites where the testing and evaluation framework has been fully applied include Puget Sound (Cullinane et al. 1986a), Indiana Harbor (USACE 1987), the New Bedford Superfund site (Francinques and Averett 1988), and the Navy Homeport at Everett, Washington (Palermo et al. 1989).
Basic Design--Detailed guidance on CDF design and operation is provided in the Corps' engineering and design manual (USACE 1987c). The most fundamental features of a CDF design are the surface area and dike height. The design of these features is dependent on the following factors:
- Quantity of material to be disposed
- Dredging and transport methods
- Operating plan
- Material physical properties
- Target raw effluent quality
The first two of these factors are self-explanatory. The operating plan is the way in which the facility is filled (e.g., in a one-time operation or in two or more operations separated by some period of time). The physical properties of the material relevant to the basic design are settling and consolidation characteristics. Recommended laboratory testing procedures for these properties are summarized in USACE (1987c). The target raw effluent quality is the maximum level of suspended solids in the primary (raw) effluent from the CDF during disposal.
The ADDAMS model is a series of computer models developed by the Corps for evaluating disposal alternatives and assisting in CDF design (Schroeder and Palermo 1990). For purposes of illustration, a hypothetical CDF design was developed using the ADDAMS model and the following assumptions:
- Design capacity: 100,000 yd (76,000 m)
- CDF shape: rectangular
- Dike construction: earthen dikes
- Dike slope: 3 horizontal, 1 vertical
- Dike crest width: 10 ft (3 m)
If the materials disposed in this hypothetical CDF are mechanically dredged and transported sediments, or residues that are of comparable solids content, the design of the CDF surface area and dike height would be relatively simple. For this hypothetical CDF, the relationship between surface area and dike height required for 100,000 yd (76,000 m) of sediments (in place) is shown in Figure 8-6. In this case, the CDF design is driven by the volume of sediments. No additional dike height is needed for ponding or settling with mechanically dredged sediments. The facility could be designed to fit within land or height restrictions, or optimized to cost. Sediment dewatering and consolidation would provide additional capacity, which might be used for more sediments or the placement of a cap/cover. The experience of the Buffalo and Detroit Districts has shown dredged material consolidation in CDFs of about 20 percent.
If the materials disposed in the CDF are hydraulically dredged or transported, the design must accommodate more variables. Because the material is contained in a slurry, the CDF design must provide adequate conditions for settling to occur, not just bulk storage capacity for the solids. The SETTLE model of ADDAMS can be used to determine the basic design of a CDF needed to achieve the target raw effluent quality. For illustration, the above hypothetical CDF was designed for hydraulic disposal using the following additional assumptions:
- Average solids concentration: 740 g/L
- Minimum freeboard: 2 ft (0.6 m)
- Depth of withdrawal: 3 ft (0.9 m)
- Percent of area ponded at end of disposal: 80 percent
- Hydraulic efficiency: 60 percent
- Target raw effluent concentration after primary settling: 1,000 mg/L suspended solids
The physical, settling, and consolidation properties of the sediments were based on laboratory tests with Indiana Harbor sediments (Environmental Laboratory 1987). Comparable data should be obtained for a detailed CDF design. For preliminary designs, Schaefer and Schroeder (1988) have compiled physical, settling, and consolidation data from dredged material from numerous locations for application to ADDAMS.
The relationship between surface area and dike height for the hypothetical upland CDF with production (dredging) rates of 1,000 and 5,000 yd (760 and 3,800 m; in place) per day is shown in Figure 8-7. By limiting the production of the dredge, the surface area requirements of the CDF can be significantly reduced. In a CDF with a fixed surface area and dike height (other factors being equal), greater production rates would result in reduced solids retention and higher levels of suspended solids in the raw effluent. The basic design of a CDF for hydraulically dredged sediments should achieve a balance among the key factors: dredge production, surface area, dike height, and raw effluent quality. The design of a CDF must therefore be interactive with the design of the dredging, transport, and residue management components of the remedial alternative.
Selection of Contaminant Controls--The types of controls selected for a CDF are determined using the Corps/USEPA testing and evaluation framework (Figure 8-5). The results from the laboratory testing described previously are used with information about the disposal site and computer models to evaluate the potential for contaminant migration and to determine the need for and efficiency of environmental controls (Francinques et al. 1985).
Computer programs that have been used to evaluate CDF environmental controls include the ADDAMS program for characterizing primary effluent quality (Schroeder and Palermo 1990) and the HELP model, developed to assist the design of landfill caps, liners, and leachate collection systems (Schroeder et al. 1984). A modified version of HELP has been developed specifically for CDFs.
The type and number of controls in a CDF design depend on the characteristics of the sediments and the site. There is no generic or default design. Available control technologies, and their application at existing CDFs, are discussed in the ARCS Program literature review (Averett et al., in prep.) and in the Corps' engineering and design manual (USACE 1987c). Designers are cautioned in applying controls commonly used at solid and hazardous waste landfills without due consideration of the physical properties of sediments and the quantities of water that may need to be drained, routed for collection, and treated.
Fine-grained sediments, when properly consolidated, can have very low permeabilities. Laboratory tests with Indiana Harbor sediments produced permeabilities on the order of 10[-8] cm/sec (Environmental Laboratory 1987). Fine-grained sediments dredged as part of sediment remediation or for other purposes might be an integral part of the contaminant controls for a CDF. For example, a CDF designed for contaminated and TSCA-regulated sediments might place the contaminated sediments in a manner that creates an additional barrier between the TSCA-regulated sediments and the outside of the CDF.
Operation and Maintenance--A detailed discussion of the construction, operation, and maintenance of CDFs is provided in Chapter 10.
Temporary Storage Facilities
The construction and operation of a temporary storage facility are regulated in the same manner as CDFs. The fact that the structure is temporary will not affect the applicability of Federal regulations such as the Clean Water Act. The requirements of State and local regulations are site specific. Some environmental regulations have restrictions on the temporary storage of materials. For example, RCRA-hazardous waste can be stored 90 days without a storage permit. Permits are issued under both RCRA and TSCA for the temporary storage of regulated hazardous and toxic wastes for up to 1 year.
Temporary storage facilities are designed to accommodate the physical and chemical characteristics of the project sediments and fulfill the needs of other components of the remedial alternative. If sediments are to be processed using a treatment technology, a facility may be needed to store the dredged sediments while awaiting pretreatment and treatment. The temporary storage facility may be used to perform some types of pretreatment, such as dewatering or physical separation. The size and capacity of the facility may be determined by several factors:
- Quantity of materials to be dredged
- Production rate of the dredging
- Pretreatment requirements of the treatment technology
- Process rate of the treatment technology
The design of a temporary storage facility is determined by the same factors that apply to CDFs. Because the facility is not permanent and will be removed when the remediation is completed, controls for long-term contaminant migration may not be necessary. However, temporary facilities should be designed with consideration of how the site will be cleared and decontaminated when the remediation is completed.
For some of the disposal technologies described in this chapter, there is no disposal cost. This means that the costs for dredging, transportation, or other components include any equipment or labor costs associated with disposal. For other disposal technologies, information is provided about disposal costs that are separate from other component costs. In this section, the equipment and effort required for each disposal technology are described, and unit costs from the literature or other project cost estimates are provided, when available. The elements of the disposal technologies and available unit costs are summarized in Table 8-4.
Unrestricted, open-water disposal is generally the least costly disposal technology for uncontaminated sediments and residues. The disposal process does not require any additional equipment, other than the equipment used for dredging and transportation, or any additional effort on the part of the contractor, other than opening the barge doors or positioning the pipeline discharge. Monitoring requirements for unrestricted, open-water disposal are site specific, but are generally limited, if any. There are, therefore, no separate costs for unrestricted, open-water disposal.
Not all of the costs of capping are covered by the dredging and transportation components. Specialized equipment, such as a submerged diffuser and sophisticated positioning equipment, may be required. The contractor will need additional time to place the material with greater levels of precision and control than necessary with unrestricted, open-water disposal.
The material for the cap and its placement can be a major cost item. If the capping is conducted in conjunction with the disposal of suitable uncontaminated sediments from another project, there may be no additional cost for the cap. This presumes that the capping material was planned to be dredged and disposed in the vicinity of the capping site with or without the remediation project. If the cap material must be furnished solely for the capping, the costs for dredging, transportation, and placement will be included in the disposal costs.
Ideally, the cap is situated in a location that is depositional, where natural settling particulate matter will deposit on the cap and further isolate the contaminated sediments. In other locations, the cap may have to be replenished periodically. The maintenance of the cap should be included in the disposal costs, unless the maintenance material is provided without cost from other dredging projects.
The monitoring requirements for capping may include periodic bathymetric surveys and camera profiles. Less frequent monitoring might also include analysis of core sediment samples and toxicity or bioaccumulation measurements (Fredette et al. 1990a,b). The type and frequency of monitoring are site specific, but the costs of monitoring and cap performance evaluation are part of the disposal costs. Experience with dredged material capping in New England indicates that routine monitoring, consisting of a bathymetric survey and a camera profile, is conducted every 2-3 years at a cost of about $30,000 per cycle (Fredette 1993).
Contained Aquatic Disposal
The cost items for contained aquatic disposal are basically the same as those described for level-bottom capping. The only additional disposal costs are related to the construction of the depression or trench for placement of contaminated material. If the contained aquatic disposal site is in deep water, the selection of dredging equipment may be limited to mechanical (bucket) dredges. If the material excavated to form the depression or trench is suitable for the cap, the cost for cap material may be offset, although there may be additional costs associated with temporarily stockpiling and rehandling the excavated material for later use as the cap material.
The placement of uncontaminated materials onto beaches will generally not require additional equipment, effort, or costs beyond those included in the dredging and transportation components. The only disposal cost would be for the earthmoving equipment and effort needed to spread the material across the beach or to form dunes.
The land application of sediments or treatment residues that have been mechanically dredged or have been suitably dewatered will generally not require additional equipment, effort, or costs beyond those included in the dredging and transportation components. The only disposal cost would be for the equipment and effort needed to spread the material, incorporate it into the existing soil, and properly grade the site. It is assumed that the landowner or local government would be responsible for any seeding or planting.
If the sediments or residues to be applied on land are hydraulically dredged or transported, additional effort and equipment will be needed to promote the retention of solids. A diked area or CDF will have to be constructed onsite. The level of sophistication for this structure would be very basic, and the only environmental controls would be related to effluent quality. Costs for dike construction are discussed for CDFs below. Costs for effluent treatment are discussed in Chapter 9.
General Construction Fill
The use of sediments or treatment residues as construction fill will generally not require additional equipment, effort, or costs beyond those included in the other remediation components. It is assumed that suitable sediments or residues would be appropriately dewatered, and the materials would be either picked up by the construction contractor or delivered to the construction site. If fill material is in demand, construction contractors may be willing to pay for the excavation and transport of sediments from a CDF.
Solid Waste Management
The use of sediments or treatment residues as daily cover or for construction in municipal or commercial landfills will generally not require additional equipment, effort, or costs beyond those included in the other remediation components. It is assumed that suitable sediments or residues would be appropriately dewatered, and the materials would be either picked up by the landfill operator or delivered to the landfill.
Costs for the disposal of contaminated materials to municipal or commercial landfills are determined by the market value of landfill space in a particular region. There are no additional equipment or effort requirements beyond those included in other remediation components. The transportation contractor will place the material as directed by the landfill operator, who will be responsible for its spreading and compaction.
Representative costs of disposal to commercial landfills in the metropolitan areas of Buffalo, Chicago, and Detroit were obtained through telephone interviews with landfill owners/operators in April, 1993, and are summarized in Table 8-5. Unit costs are based on weight ($/ton) or volume ($/yd). Although a landfill operator is ultimately basing the quoted price on how much capacity (volume) the disposed material will require, many operators are now using weight-based payment because it can be measured more accurately at delivery (Payne 1993).
The landfill unit costs that are based on weight are consistently higher than unit costs based on volume. This is because the majority of materials disposed in commercial landfills have a density of less than 1 tonne/yd. Residential and commercial solid wastes (uncompacted) typically have densities less than 0.5 tonne/yd (Tchobanoglous et al. 1977).
The weight of a given volume of sediments or treatment residues will depend on its grain size distribution, solids content, and amount of organic material. A typical saturated sediment (50 percent solids) with about 70 percent silt and clay and 10 percent organic material (volatile solids) would probably weigh about 2,400-2,700 lbs/yd (1,400-1,600 kg/m).
Because the density of sediments and treatment residues is much higher than that of most materials disposed in commercial landfills, the weight-based unit costs may not accurately reflect market price. The volume-based unit costs are probably more representative. Therefore, landfill owners/operators should be provided information about the density and other physical properties of the sediments or residues in order to form a competitive unit cost.
As discussed above, landfills may accept sediments for beneficial use as daily cover. Depending on the local availability of cover material, the landfill may accept the material at no cost or offer a price discount. The discount should be approximately equal to the amount the landfill has to pay for daily cover from other sources. Most of the landfill operators contacted indicated a willingness to offer a price discount. A discount of $10/ton was offered by one operator. Some states or municipalities have restrictions on the type of material used for daily cover at landfills.
Confined Disposal Facilities
The principal elements of the capital costs for a CDF include:
- Engineering and design costs
- Lands and easements
- Materials for dikes
- Materials for contaminant controls
- Construction equipment and labor costs
Of these elements, the costs for lands and materials for dikes and contaminant controls typically are the highest of the capital costs. As an illustration, the capital costs of hypothetical, upland CDFs with a design capacity of 100,000 yd (76,000 m) were estimated for two sizes and three contaminant control system designs. The CDFs had the same basic design assumptions discussed earlier in this chapter, with the following unit costs provided by Corps district personnel as being representative of the Great Lakes region:
- Cost of land: $10,000/acre ($24,700/hectare)
- Cost of dike material (constructed): $3/yd ($4/m)
- Cost of clay (compacted): $3/yd ($4/m)
- Cost of plastic liner (70 mil): $1.5/ft ($16/m)
- Cost of leachate collection system (4-in. [10-cm] polyvinyl chloride): $5/linear ft ($16/linear m)
- Cost of sand/gravel: $12/yd ($16/m)
Figure 8-8 also compares the capital costs for these CDFs with earthen dikes and no cap or liner (no control system) to identical facilities with RCRA Subtitle C and RCRA Subtitle D control systems (as depicted in Figure 8-3). The costs of these types of controls increases with CDF surface area. The costs shown in Figure 8-8 do not include the costs for engineering and design, construction oversight, permits, or systems for treating effluent or leachate. The costs shown reflect facilities where dike and contaminant control materials had to be imported. Sites with native soils suitable for dike construction would have lower costs. The availability of clay for contaminant barriers (e.g., liners and caps) can also affect CDF costs.
The most complete actual costs for CDF construction are available for the facilities constructed by the Corps around the Great Lakes under the authority of the Rivers and Harbors Act of 1970 (PL 91-611), section123. These costs, shown in Figure 8-9, represent the construction contract costs for facilities constructed between 1970 and 1988, adjusted to January 1993 costs using ENR's CCI. Figure 8-9 shows unit costs ($/yd) for CDFs vs. total CDF capacity. CDFs are also indicated as being upland or in-water. These costs do not include the costs for engineering and design, construction oversight, or permits, but may include costs for effluent treatment systems (e.g., weirs and filter cells). The CDF costs shown do not include any costs for land acquisition, which was a requirement of local sponsors under this authority.
Although there is a general trend showing the economy of scale (lower unit costs for larger CDFs), the variation attributable to site-specific conditions and designs (as indicated by the amount of scatter) predominates..
Temporary Storage Facilities
The costs for a temporary storage or rehandling facility can be estimated using the capital cost information for CDFs provided above. The types of contaminant controls in a temporary facility may be less stringent than those designed for a permanent CDF. Land costs may not be appropriate if a limited easement or right-of-way is obtained. Long-term maintenance costs would also not be incurred.
An additional cost for temporary facilities would result from the demolition of the structures and decontamination of the site. Materials that have contacted contaminated sediments or residues may have to be treated or disposed in the same manner as the sediments.
Disposal technologies have more mechanisms for contaminant loss than most other remediation components. Procedures to estimate contaminant losses from disposal technologies are also more developed than for other components, primarily as a result of research conducted by the Corps in relation to dredged material disposal and broad-based research on landfills of all types. Myers et al. (in prep.) provides a summary of predictive tools for estimating contaminant losses from sediment disposal technologies.
Contaminant loss pathways of concern for open-water disposal technologies are different from those for beneficial use and confined disposal. One of the primary differences is the movement of dredged material through the water column and subsequent water column impacts associated with open-water disposal. Beneficial use and confined disposal technologies usually do not involve the type of direct water column impacts associated with open-water disposal.
Contaminant migration pathways for beneficial uses and confined disposal alternatives are similar because both types of disposal options involve some type of confinement in most cases. There is always a potential for leachate and volatile loss pathways to be of concern when considering beneficial use and confined disposal. In addition, hydraulic placement will involve an effluent pathway for both beneficial use and confined disposal. The relative significance of plant and animal uptake depends on the ultimate use and engineering design of the disposal site.
Within a sediment remedial alternative, unrestricted, open-water disposal is feasible only for sediments or residues that have been decontaminated. Regulatory testing procedures to determine if dredged or fill materials are suitable for unrestricted, open-water disposal are contained in USEPA/USACE (1990) for ocean disposal and in USEPA/USACE (1994) for disposal to inland and near coastal waters.
Capping and contained aquatic disposal may be viable disposal technologies for contaminated sediments or residues from treatment technologies. Procedures for evaluating the acceptability of capping and contained aquatic disposal technologies are identified in USACE/USEPA (1992). The main objectives are to determine water column impacts during dredged material placement and impacts on benthic organisms after placement. The procedures for evaluating water column impacts can be adapted to estimating contaminant losses. Equipment to reduce water column impacts (i.e., tremies and submerged diffusers) is available. Controls on benthic impacts are generally the primary concern in determining cap design.
In addition to water column and benthic impacts associated with capping and contained aquatic disposal, there is a potential for contaminant loss associated with diffusion through caps. Techniques for estimating diffusion losses are described in Myers et al. (in prep.). The information needed for estimating diffusion losses is described in Chapter 3, Nonremoval Technologies. Some type of mathematical tool (e.g., spreadsheets, numerical models, commercially available software for performing mathematical calculations) is needed to solve the model equations described in Myers et al. (in prep.).
For beneficial use technologies, the potential for plant and animal uptake of contaminants can be a major concern. Some beneficial uses, such as construction fill, may eliminate plant and animal uptake pathways through engineering design.
Solid waste management uses (daily sanitary landfill cover) also may not involve plant and animal uptake pathways, unless the material is used as final cover. The contributions of contaminated sediments or treatment residues to leachate generation can be a concern for solid waste uses. Because sanitary landfills are now required to be lined, groundwater impacts should be minimal if the landfill is properly designed and constructed.
Volatile emissions will be a major factor for land application alternatives. In a land application scenario, volatilization may potentially account for more loss than any other mechanism, depending on the chemical properties and land application operations. For this reason, worker health and safety and air quality impacts are potential concerns for land application of sediments or treatment residues containing certain organic chemicals.
Leachate and volatile loss pathways are potentially significant for most sediment remedial alternatives, including those involving beneficial use. Construction fill and solid waste management use alternatives are especially likely to require evaluation of these losses. Because the basic mechanisms by which contaminants are lost along these pathways are the same for beneficial uses and CDFs, the estimation techniques developed for CDFs (Myers et al., in prep.) can be applied to beneficial uses. Modification of procedures and interpretation may be appropriate, depending on project-specific conditions.
Contaminant migration pathways for an upland CDF are shown in Figure 2-6. Pathways involving movement of large masses of water, such as CDF effluent during hydraulic filling, have the greatest potential for releasing significant quantities of contaminants from CDFs. Pathways such as volatilization may also result in the release of organic chemicals in highly contaminated dredged material at certain stages in the filling of a CDF. Techniques for estimating effluent, leachate, and volatile losses are described in Myers et al. (in prep.).
If dredged material is placed hydraulically, effluent will be a temporary, but major, contaminant loss pathway. Effluent from a CDF is considered a dredged material discharge under section 404 of the Clean Water Act and is also subject to water quality certification under section 401. Losses along this pathway can be controlled by proper design of the disposal site, management of disposal operations for minimizing losses, and effluent treatment. Techniques for estimating effluent losses are described in Myers et al. (in prep.). Modified elutriate and column settling tests (see Table 8-3) are required for CDF design and effluent loss calculations.
Subsurface seepage from CDFs may reach adjacent aquifers or enter surface waters. Fine-grained sediments tend to form their own disposal-area liner as they settle and consolidate. Evaluation of leachate quality from a CDF must include a prediction of which contaminants may leach and the mass release potential. Laboratory procedures are available for prediction of leachate quality (Myers et al. 1992). These procedures are based on theoretical analysis of laboratory batch and column leach data. Experimental testing procedures only provide data on leachate quality. Estimates of leachate quantity must be made by considering site-specific hydrology. Computerized procedures such as the USEPA HELP model (Schroeder et al. 1984) can be used to estimate water balance for CDFs (Myers et al., in prep.).
The potential for volatile emissions should be evaluated in cases where sediments contain volatile or semivolatile organic compounds. Volatile emissions should be evaluated to protect workers and others who could inhale contaminants released through this pathway. Although no laboratory procedures for measuring volatilization from dredged sediments have been developed, volatile flux equations based on chemical vapor equilibrium concepts and transport phenomena fundamentals are available for estimating volatile losses (Myers et al., in prep.). Volatile emission rates are primarily dependent on the chemical concentration in the dredged material, the surface area through which emission occurs, and climatic factors such as wind speed.
Some contaminants in exposed dredged material can bioaccumulate in plant and animal tissue and become further available to the food web. Prediction of uptake is based on plant or animal bioassays (Folsom and Lee 1985; Simmers et al. 1986). Contaminants in plant or animal tissue are chemically analyzed, and the results are compared with Federal criteria for food or forage. Management strategies can be formulated to minimize plant and animal uptake by directing where to place dredged material (e.g., using cleaner materials to cover more contaminated materials).
Immediately after dredged material placement (beneficial use or confined disposal) and after ponding water is drawn down, rainfall may generate contaminated runoff from the settled dredged material. Presently, there is no simplified procedure for predicting runoff quality. A soil lysimeter testing protocol (Lee and Skogerboe 1983) has been used to predict surface runoff quality with good results. If runoff concentrations exceed standards, appropriate controls may include placement of a cap, maintenance of ponded water conditions (although this may conflict with other management goals), vegetation to stabilize the surface, treatments such as liming to raise the pH, and treatment of the runoff (as for effluent).